Many organic polymeric materials on and after exposure to light, especially ultraviolet (UV) light, degrade as shown by yellowing, embrittlement, and eventual breakdown of the polymeric materials. Common step growth polymers such as polyesters and polyurethanes are vulnerable, especially to UV light, and it has long been a practice to blend small amounts of UV stabilizers into thermoplastic polymers to arrest or inhibit such degradation.
Among the classes of UV stabilizers used are 2-hydroxybenzophenones and their derivatives, which, when blended with polymers, have been partially effective in their ability to arrest UV degradation. Unfortunately, significant amounts of these stabilizers can be lost from the polymers due to blooming, exudation, volatilization, solvent extraction during fabrication and cleaning, and in other end uses. The problem is most severe in articles which have a high surface area to volume ratio, such as fibers and films.
Direct introduction of the 2-hydroxybenzophenone moiety into polymers to prevent or arrest UV degradation has been taught. U.S. Pat. No. 3,391,110 describes copolymerizable 2-hydroxybenzophenones; however, they possess only one polymerizable group and thus can serve only to terminate a polymer or growing polymer chain. This limits both the molecular weight of the polymer and its useful mechanical properties.
U.S. Pat. Nos. 3,366,668, 3,385,910, 4,189,409, 4,354,016, and 4,456,746, describe polymers containing the 2-hydroxybenzophenone moiety and U.S. Pat. No. 4,284,756 describes a polymer containing the 1-hydroxy-xanth-9-one moiety wherein these moieties are part of the backbone of the polymer chain.